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Commit f651bd96 authored by Daniel Axtens's avatar Daniel Axtens Committed by Herbert Xu
Browse files

crypto: vmx - Document CTR mode counter width quirks 



The CTR code comes from OpenSSL, where it does a 32-bit counter.
The kernel has a 128-bit counter. This difference has lead to
issues.

Document it.

Signed-off-by: default avatarDaniel Axtens <dja@axtens.net>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 334d37c9

drivers/crypto/vmx/aesp8-ppc.pl

+20 −2
Original line number Diff line number Diff line
@@ -1286,6 +1286,24 @@ ___ 


#########################################################################

{{{	# CTR procedure[s]						#



####################### WARNING: Here be dragons! #######################

#

# This code is written as 'ctr32', based on a 32-bit counter used

# upstream. The kernel does *not* use a 32-bit counter. The kernel uses

# a 128-bit counter.

#

# This leads to subtle changes from the upstream code: the counter

# is incremented with vaddu_q_m rather than vaddu_w_m. This occurs in

# both the bulk (8 blocks at a time) path, and in the individual block

# path. Be aware of this when doing updates.

#

# See:

# 1d4aa0b4c181 ("crypto: vmx - Fixing AES-CTR counter bug")

# 009b30ac7444 ("crypto: vmx - CTR: always increment IV as quadword")

# https://github.com/openssl/openssl/pull/8942

#

#########################################################################

my ($inp,$out,$len,$key,$ivp,$x10,$rounds,$idx)=map("r$_",(3..10));

my ($rndkey0,$rndkey1,$inout,$tmp)=		map("v$_",(0..3));

my ($ivec,$inptail,$inpperm,$outhead,$outperm,$outmask,$keyperm,$one)=
@@ -1357,7 +1375,7 @@ Loop_ctr32_enc: 
	addi		$idx,$idx,16

	bdnz		Loop_ctr32_enc



	vadduqm		$ivec,$ivec,$one

	vadduqm		$ivec,$ivec,$one	# Kernel change for 128-bit

	 vmr		$dat,$inptail

	 lvx		$inptail,0,$inp

	 addi		$inp,$inp,16
@@ -1501,7 +1519,7 @@ Load_ctr32_enc_key: 
	$SHL		$len,$len,4



	vadduqm		$out1,$ivec,$one	# counter values ...

	vadduqm		$out2,$ivec,$two

	vadduqm		$out2,$ivec,$two	# (do all ctr adds as 128-bit)

	vxor		$out0,$ivec,$rndkey0	# ... xored with rndkey[0]

	 le?li		$idx,8

	vadduqm		$out3,$out1,$two